The present invention relates to an automatic paper feeder for an image forming apparatus, such as a printer, a copying machine, and facsimile equipment.
FIG. 39 is a cross sectional view illustrating a conventional automatic paper feeder disclosed in, for example, Japanese Patent Application Laid-Open No. 221033/1990. In the drawing, reference numeral 1 denotes paper; 2 denotes a paper cassette for accommodating the paper 1; 3 denotes a pick roller for picking out the paper 1 in the paper cassette 2; 4 denotes a separation roller for separating the sheets of paper 1 picked out by the pick roller 3 and feeding the paper 1 one sheet at a time; and 5 denotes a coil spring serving as an urging means for causing the paper 1 in the paper cassette 2 to abut against the pick roller 3.
Next, a description will be given of the operation. A leading end portion of the paper 1 in the paper cassette 2 is pushed upward by the coil spring 5, and an uppermost sheet of paper 1 abuts against a lower surface portion of the pick roller 3. In addition, the separation roller 4 is disposed in such a manner as to rotate in contact with the pick roller 3. When the pick roller 3 is rotated in the traveling direction of the paper in the above-described state, the paper 1 is taken out from inside the paper cassette 2.
In cases where one sheet of paper 1 has been taken out from inside the paper cassette 2, since the force for transporting the paper 1 due to a frictional force between the pick roller 3 and the paper 1 is set in such a manner as to overcome the separating torque of the separation roller 4 acting in the direction of the arrow indicated by the broken line, the separation roller 4 rotates by following the rotation of the pick roller 3, thereby feeding the paper 1 to an ensuing step.
In the event that two sheets of paper 1 have been taken out from inside the paper cassette 2, since the separating torque of the separation roller 4 is set in such a manner as to overcome the frictional force between the two sheets of paper 1, the separation roller 4 separates the sheets of paper 1 by rotating in the direction of the arrow indicated by the broken line, thereby feeding only one sheet of paper 1 to the ensuing step.
However, with the arrangement of the automatic paper feeder shown in FIG. 39, since the separation roller 4 constantly abuts against the pick roller 3, the following drawback has been encountered. If the separated paper 1 is not returned to inside the paper cassette 2 and remains located in the vicinity of a paper separating portion 19, i.e., a portion of contact between the pick roller 3 and the separation roller 4, unless the rotation of the pick roller 3 is stopped immediately after a trailing end of the paper 1, fed out in the form of only one sheet after being separated, has passed the separating portion 19, an overlapped feeding of paper can occur in which the separated paper 1 remaining in the vicinity of the separating portion 19 is also transported by following the paper 1 fed out in the form of only one sheet after being separated.
In addition, since a rotational torque is constantly produced in the separation roller 4 in an opposite direction to the traveling direction of the paper 1, if the separation roller 4 is in the state in which the separation roller 4 constantly abuts against the pick roller 3, there is a possibility that a difference in speed can occur between the traveling speed of the paper 1 and the peripheral speed of the separation roller 4 at the surface of contact between the paper 1 and the separation roller 4 when one sheet of paper 1 is being transported. Hence, there has been a drawback in that defects, such as damage or roller scars caused to the paper 1, can occur due to the difference in speed.
In addition, with the arrangement of the automatic paper feeder shown in FIG. 39, since the leading end portion of the paper 1 in the paper cassette 2 is constantly pushed upward by the coil spring 5, and an uppermost sheet of paper 1 constantly abuts against a lower surface portion of the pick roller 3, there is a drawback in that an overlapped feeding of the paper can occur because there is always a possibility of the paper 1 in the paper cassette 2 being taken out while the pick roller 3 is rotating in the traveling direction of the paper 1.
In addition, since the arrangement provided is such that the paper 1 in the paper cassette 2 is pushed upward by the coil spring 5, and the paper 1 is made to abut against the lower surface portion of the pick roller 3,, the pressure-contacting force at the time when the paper 1 is brought into contact with the lower surface portion of the pick roller 3 is determined by the coil spring 5. Further, the pressure-contacting force varies depending on the amount of the paper 1 loaded in the paper cassette 2 and the kind of paper 1, so that there are limitations to the kinds of paper that can be used.
In addition, because the force with which the pick roller 3 takes out the paper 1 from the interior of the paper cassette 2 is unstable, there has been a problem in that the misfeeding of the paper can possibly occur.